PEM fuel cells (Polymer Electrolyte Membrane fuel cells) are electrochemical cells which, to simplify, comprise anode and cathode with interposed polymeric solid electrolyte. In order to operate such cells, fuels are continuously applied to both electrodes from the exterior, said fuel being there electrochemically converted, so that a current can be derived at the electrodes. It is now at present however, impossible to convert all of the chemical energy supplied. During operation of the fuel cell a certain proportion is always lost as heat. For this reason, higher-performance fuel cells require measures for heat removal. This is effected according to prior art by electrically conductive heat exchanger plates through which a cooling fluid flows (Literature: A. J. Appley, E. B. Yeager, Energy 11, 137.152 1986!).
In this case both sides of the membrane-electrode unit are in contact with the electrically conductive plates, interposed seal rings being used in order to achieve a tightness of the cell. The conductor plates are designed as heat exchangers, i.e. they contain ducts through which a cooling fluid flows. The cooling fluid is fed in and out through openings in the plate. Furthermore, feed and return ducts for the fuels are integrated in the electrically conductive plates, the fuels then being supplied through suitable structures to the electrodes. It is however necessary for such a fuel cell construction according to prior art for the plates to consist of electrically conductive material, as each plate must press against the respective electrode surface in order to produce the outward electrical contact of the cell. In the case of a stack structure, the plates can also be constructed as bipolar plates.
In order to achieve higher performance and particularly in order to achieve a higher voltage, it is also known to incorporate together a plurality of membrane-electrode units as described above to form a so-called fuel cell stack (U.S. Pat. No. 4,175,165 "Fuel cell system utilizing ion exchange membranes and bipolar plates"). For this purpose until now a plurality of cells as described above were separately constructed, disposed one behind the other and incorporated electrically in series, so that the voltages of the individual cells are added to one another. The constructive outlay for such an in-series incorporation is however extremely high, as each membrane-electrode unit must have a separate fuel supply. The result is an extremely high constructive outlay for these cells.